Method for producing composite powders based on silver-tin oxide, the composite powders so produced, and the use of such powders to produce electrical contact materials by powder metallurgy techniques

a technology of silver-tin oxide and composite powders, which is applied in the direction of liquid/solution decomposition chemical coatings, coatings, transportation and packaging, etc., can solve the problems of limited powder particle size, significant changes in processing and contact properties, and difficult to predict in terms of size and tendency

Inactive Publication Date: 2001-12-13
UMICORE AG & CO KG +1
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

The method can be used either wet or dry, for instance with water, alcohol, etc., but is limited to powders having a particle size greater than 1 .mu.m.
Manufacture of these preferred contact materials has up to now taken place only using the internal oxidation process, which is costly.
However, this technique can only be used with the typically used oxides if special measures are taken.
These different processes produce different structural formations in the metal and oxide phases of the silver matrix; produce significant changes in the structure-dependent material properties; and thus produce significant changes in the processing and contact properties, which are difficult to predict in terms of size and tendency.
Thus, considerable differences wit

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  • Method for producing composite powders based on silver-tin oxide, the composite powders so produced, and the use of such powders to produce electrical contact materials by powder metallurgy techniques

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Embodiment Construction

[0036] To produce a 4-kg batch of a composite powder for the contact material Ag--SnO.sub.2--In.sub.2O.sub.3, having about 9 wt % SnO.sub.2 and about 3 wt % In.sub.2O.sub.3, with extremely high oxide dispersion in the silver matrix, equivalent amounts of the starting powders of the oxides, with an average particle size of D.sub.50=0.7 .mu.m, are suspended in 3 L of deionized water, by means of a disperser, over a period of 30 min., at room temperature, and then stirred into 18 L of deionized water in a 50-L reaction vessel. By the simultaneous and uniform feed of stoichiometric amounts of 3.5 mol silver nitrate and 1.7 mol ascorbic acid solutions through two separate connections (see FIG. 1), with simultaneous thorough mixing using a high energy stirrer system, metallic silver is precipitated onto the oxide particles at a constant rate of about 130 g / min. The temperature in the reaction vessel is limited to 40.degree. C. through cooling. The precipitation products produced in this w...

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Abstract

A method for producing composite powders based on silver-tin oxide, by chemically reductive precipitation of silver onto particulate tin oxide. A solution of a silver compound and a solution of a reducing agent are simultaneously added in stoichiometrically equivalent amounts, separately and continuously with intensive mixing, to an aqueous suspension of tin oxide. The resulting composite powders have very high homogeneity, and can be processed to make electrical contact materials. The method is particularly suitable for producing composite powders based on silver-tin oxide doped with indium oxide, to be used in the manufacture of electrical contact materials.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to composite powders based on silver-tin oxide, and to methods for making them. The invention relates also to electrical contact materials made from such composite powders.[0003] 2. Description of the Related Art[0004] Electrical contact materials typically consist of silver with certain metal and / or oxide additives. These materials are made using powder metallurgy techniques.[0005] The materials are chosen based on the intended use, such as the type of switching device, the switching current, and the electrical load. General requirements include low electrical wear with high arc resistance, and low weld force with low contact resistance.[0006] The air contactors of low voltage / high current equipment, within a switching current range of 100-3000 A, are primarily made with materials based on silver-tin oxide, in which the oxide content, in practice, lies between about 8 and 12 wt. %. Contact materials of this type g...

Claims

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Application Information

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IPC IPC(8): B22F1/18B22F9/24C22C32/00C23C18/16H01H1/02H01H1/0237
CPCB22F1/025B22F9/24C22C32/0021H01H1/02376B22F1/18B22F3/12
Inventor WOLMER, ROGERMUELLER, MECHTHILDHERINGHAUS, FRANKRUEHLICKE, DIETRICHGOIA, DAN
Owner UMICORE AG & CO KG
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